NEW YORK — The man charged with killing a 6-year-old boy in 1979 made a false confession and will plead not guilty in a case that catalyzed the missing-children’s movement, his attorney said Thursday.

Pedro Hernandez’s admission in May to suffocating Etan Patz was a stunning turn in one of the most notorious and vexing cases in New York City history, prompting the first arrest ever in the case. But he is mentally ill, and his statements “are not reliable,” said his attorney, Harvey Fishbein, after Hernandez, 51, made a brief court appearance Thursday.

“The really sad part of this case is that it will take time, it will take money … and it will not tell the city what happened to Etan Patz,” Fishbein said.

But prosecutors say an exhaustive post-arrest investigation found enough evidence to seek an indictment and proceed to trial. A judge set a Dec. 12 date for Hernandez to enter a plea.

As news of the deadly mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, unfolded last week, Pia Guerra, a 46-year-old Vancouver-based artist, felt helpless. She couldn’t bring herself to go to sleep, so she began to draw.

Police who find suspected drugs during a traffic stop or an arrest usually pause to perform a simple task: They place some of the material in a vial filled with liquid. If the liquid turns a certain color, it’s supposed to confirm the presence of cocaine, heroin or other narcotics.